Semiconductor device and method of manufacturing the same

ABSTRACT

A semiconductor device that reduces the deformation of a metal base due to pressure during transfer molding, to thereby suppress the occurrence of cracks in an insulating layer to achieve high electrical reliability. The semiconductor device includes: a metal member provided, on its lower surface, with a projection and a depression, and a projecting peripheral portion surrounding the projection and the depression and having a height greater than or equal to a height of the projection of the projection and the depression; an insulating layer formed on an upper surface of the metal member; a metal layer formed on an upper surface of the insulating layer; a semiconductor element joined to an upper surface of the metal layer; and a sealing resin to seal the semiconductor element, the metal layer, the insulating layer and the metal member.

TECHNICAL FIELD

The present invention relates to a fin-integrated semiconductor devicehaving a simple structure with good heat dissipation properties andquality, and a method of manufacturing the same.

BACKGROUND ART

A conventional semiconductor device has a semiconductor element, whichis a heat generating component, mounted thereon. The semiconductorelement generates heat when the semiconductor device is driven. Toimprove dissipation of this heat, a thick metal substrate or ceramicsubstrate provided with a circuit pattern is used. In addition, toincrease a heat dissipation area to improve the heat dissipation, a finbase including heat dissipation fins is screwed and joined to the metalsubstrate with an insulative silicone-based resin material such asgrease interposed therebetween, for example.

A semiconductor device thus configured, however, requires a step ofapplying the silicone-based resin material to a surface of the metalsubstrate or ceramic substrate or of a heat dissipation member,resulting in an increased number of manufacturing steps. Furthermore,heat dissipation properties deteriorate due to the silicone-based resinmaterial interposed between the metal substrate or ceramic substrate andthe fin base.

Therefore, as a technique that does not include the resin materialinterposed as described above, for example, there has been proposed asemiconductor device which includes a ceramic substrate mounted on ametal plate with fins, and which is entirely sealed with epoxy resin(for example, PTD 1 and PTD 2).

CITATION LIST Patent Documents

PTD 1: Japanese Patent Laying-Open No. 2009-177038 (Page 7, FIG. 1)

PTD 2: Japanese Patent Laying-Open No. 9-22970 (Page 2, FIG. 3)

SUMMARY OF INVENTION Technical Problem

A conventional semiconductor device, which is resin-molded by transfermolding, is characterized by excellent mass productivity and long-termreliability. However, when a semiconductor device including a metal baseplate having projections and depressions on its one surface isresin-molded by transfer molding, a die needs to have an engravedstructure for protecting the projections and depressions without causingresin leakage to the projections and depressions. To prevent the resinleakage to the projections and depressions in consideration of amanufacturing dimensional tolerance for the projections as well, aclearance is needed at the engraved portion of the die between the tipsof the projections and a die surface. As a result, the metal base plateis deformed due to temperature and pressure during the resin molding,causing cracks to occur in an insulating layer to deteriorate theinsulation properties.

This invention was made to solve the problems as described above, andprovides a semiconductor device capable of reducing the deformation of ametal base due to pressure during transfer molding, to thereby suppressthe occurrence of cracks in an insulating layer to achieve improvedelectrical reliability.

Solution to Problem

A semiconductor device according to this invention includes: a metalmember provided, on its lower surface, with projections and depressionsaligned such that surfaces of the projections in a width direction faceone another in one direction, a projecting peripheral portionsurrounding the projections and the depressions and having a heightgreater than or equal to a height of the projections of the projectionsand the depressions, and projections provided in the depressions of theprojections and the depressions in a direction intersecting theprojections and the depressions and having a height greater than aheight of bottom surfaces of the depressions of the projections and thedepressions and smaller than the height of the projections of theprojections and the depressions; an insulating layer formed on an uppersurface of the metal member; a metal layer formed on an upper surface ofthe insulating layer; a semiconductor element joined to an upper surfaceof the metal layer; and a sealing resin to seal the semiconductorelement, the metal layer, the insulating layer and the metal member.

Advantageous Effects of Invention

According to this invention, since the projecting peripheral portion isprovided to surround the projection and the depression formed on thelower surface of the metal base plate, the occurrence of cracks in theinsulating layer formed on the upper surface of the metal base plate canbe suppressed, thereby improving the reliability of the semiconductordevice.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional structural diagram of a semiconductordevice in a first embodiment of this invention.

FIG. 2 is a schematic planar structural diagram of a metal base plate inthe first embodiment of this invention.

FIG. 3 is a schematic diagram of a heat dissipation fin in the firstembodiment of this invention.

FIG. 4 is a schematic diagram of another heat dissipation fin in thefirst embodiment of this invention.

FIG. 5 is a schematic diagram of another heat dissipation fin in thefirst embodiment of this invention.

FIG. 6 is a schematic diagram of another heat dissipation fin in thefirst embodiment of this invention.

FIG. 7 is a schematic sectional structural diagram of another metal baseplate in the first embodiment of this invention.

FIG. 8 is a schematic planar structural diagram of the another metalbase plate in the first embodiment of this invention, as seen from itslower surface side.

FIG. 9 is a schematic planar structural diagram of another metal baseplate in the first embodiment of this invention.

FIG. 10 shows schematic structural diagrams of another metal base platein the first embodiment of this invention.

FIG. 11 is a schematic diagram of another heat dissipation fin in thefirst embodiment of this invention.

FIG. 12 is a schematic diagram of another heat dissipation fin in thefirst embodiment of this invention.

FIG. 13 is a schematic diagram of another heat dissipation fin in thefirst embodiment of this invention.

FIG. 14 is a schematic diagram of another heat dissipation fin in thefirst embodiment of this invention.

FIG. 15 shows the shape of a swaging portion of the heat dissipation finof the metal base plate in the first embodiment of this invention.

FIG. 16 is a schematic sectional structural diagram of a step ofmanufacturing the semiconductor device in the first embodiment of thisinvention.

FIG. 17 is a schematic sectional structural diagram of a step ofmanufacturing the semiconductor device in the first embodiment of thisinvention.

FIG. 18 is a schematic sectional structural diagram of a step ofmanufacturing the semiconductor device in the first embodiment of thisinvention.

FIG. 19 is a schematic sectional structural diagram of a step ofmanufacturing the semiconductor device in the first embodiment of thisinvention.

FIG. 20 is a schematic sectional structural diagram of a step ofmanufacturing the semiconductor device in the first embodiment of thisinvention.

FIG. 21 is a schematic sectional structural diagram of a step ofmanufacturing the semiconductor device in the first embodiment of thisinvention.

FIG. 22 shows schematic sectional structural diagrams during transfermolding in the first embodiment of this invention.

FIG. 23 is a schematic sectional structural diagram during anothertransfer molding in the first embodiment of this invention.

FIG. 24 is a schematic planar structural diagram of a metal base platehaving a conventional structure.

FIG. 25 is a schematic sectional structural diagram of the metal baseplate having the conventional structure.

FIG. 26 shows schematic sectional structural diagrams during transfermolding using the metal base plate having the conventional structure.

FIG. 27 is a schematic sectional structural diagram of a semiconductordevice in a third embodiment of this invention.

DESCRIPTION OF EMBODIMENTS

Embodiments of a semiconductor device according to the present inventionwill be described below in detail based on the drawings. It should benoted that the present invention is not limited to the followingdescription, and can be modified as appropriate without departing fromthe scope of the present invention.

First Embodiment

FIG. 1 is a schematic sectional structural diagram of a semiconductordevice in a first embodiment of this invention. It should be noted thatFIG. 1 is a sectional view schematically showing a configuration of thesemiconductor device, and therefore shows positional relation ofrespective parts, components, and the like in an overview manner.

In the figure, a semiconductor device 100 includes a semiconductorelement 1, a metal base plate 2 which is a metal member, an insulatingsheet 3 which is an insulating layer, a metal wiring pattern 4 which isa metal layer, a sealing resin 5, a heat dissipation fin 6 which is afin, a peripheral portion 7, a projection 81, and a depression 82. Asshown, an X direction represents the width, a Y direction represents thethickness, and a Z direction represents the height.

A power control semiconductor element such as a MOSFET (Metal OxideSemiconductor Field Effect Transistor) or an IGBT (Insulated GateBipolar Transistor), a reflux diode, or the like is used assemiconductor element 1.

Metal base plate 2 has the functions of a metal substrate (insulationproperties and heat dissipation properties) by including insulatingsheet 3 on its upper surface (one surface). Metal base plate 2 alsoincludes a projection and a depression 8 having projection 81 anddepression 82 on its lower surface (the other surface) exposed atsealing resin 5. A region sandwiched between projection 81 andprojection 81 serves as depression 82. Metal base plate 2 has, owing toits uneven shape provided by projection and depression 8, the functionof permitting heat dissipation fin 6 to be inserted therein. Thus, anamount of projection (height) of projection 81 does not need to have thelength of the heat dissipation fin. Since the heat dissipationproperties only need to be ensured by inserting heat dissipation fin 6into semiconductor device 100, projection 81 only needs to have a heightnecessary for the insertion of heat dissipation fin 6. Depression 82only needs to have a thickness (space) into which heat dissipation fin 6can be inserted.

Furthermore, if the amount of projection (height) of projection anddepression 8 is adequate in terms of thermal capacity of semiconductordevice 100, this projection and depression 8 may play a role as a heatdissipation fin. The lower surface of metal base plate 2 is providedwith projecting peripheral portion 7 to surround this projection anddepression 8.

Furthermore, metal base plate 2 is made of a metal material having highthermal conductivity and good heat dissipation properties, such asaluminum or copper, and includes insulating sheet 3 made ofthermosetting resin such as epoxy resin on its upper surface opposite tothe surface provided with projection and depression 8.

Insulating sheet 3 is formed, for example, by filling thermosettingresin such as epoxy resin with inorganic powders such as silica,alumina, boron nitride, or aluminum nitride, used either alone or as amixture, which has high thermal conductivity for improving the heatdissipation properties.

Insulating sheet 3 having higher heat dissipation properties is oftenmore highly filled with the inorganic powders, and needs to be heated,pressed and cured at higher pressure in order to ensure its inherentthermal conductivity and insulation properties.

Metal wiring pattern 4 is pattern-formed on insulating sheet 3 byetching and the like, and is made of copper, for example. An electroniccomponent such as semiconductor element 1 is joined and mounted on thismetal wiring pattern 4 with solder (not shown). Metal wiring pattern 4and semiconductor element 1 are electrically connected by a bonding wire(not shown). It should be noted that semiconductor element 1 is notlimited to Si (silicon), and may be SiC (silicon carbide) or the likethat permits operation at high temperature. A metal wire such as aribbon or DLB may be used, other than the bonding wire, as long as metalwiring pattern 4 and semiconductor element 1 can be electricallyconnected.

Sealing resin 5 is a molding member made of epoxy-based resin andprovided to cover the top of insulating sheet 3 including the componentssuch as semiconductor element 1, and doubles as a case of semiconductordevice 100. As shown in FIG. 1, it is preferable that the area coveredby sealing resin 5 be not only on the upper surface side of metal baseplate 2, but also on the side surfaces of metal base plate 2 (sidesurfaces of peripheral portion 7). Such a structure prevents warpage andthe occurrence of cracks in semiconductor device 100 due to thermalstress and the like, leading to improved reliability.

While not particularly limited, a material for sealing resin 5 ispreferably a material filled with inorganic powders such as silica tohave a thermal expansion coefficient closer to the thermal expansioncoefficient of copper, semiconductor element 1 and the like, in order tosuppress the warpage of the entire semiconductor device 100, or, whenheat dissipation fin 6 is intended to be swaged later, is preferablyepoxy-based resin having mechanical strength to resist breakage understress such as a press pressure during the swaging.

Heat dissipation fin 6 is inserted into depression 82 of projection anddepression 8 of metal base plate 2. Heat dissipation fin 6 can be fixedto depression 82 by an insertion method using swaging, brazing, or afixing member. Heat dissipation fin 6 does not need to have a widthmatching the width of projection and depression 8 of metal base plate 2,and can have an insertable shape with respect to the shape of projectionand depression 8 of metal base plate 2, thereby further improving theheat dissipation properties of semiconductor device 100. To fix heatdissipation fins 6 by swaging, heat dissipation fins 6 are alternatelydisposed for every plurality of depressions.

FIG. 2 is a schematic planar structural diagram of the metal base platein the first embodiment of this invention. FIG. 2 is a schematic planarstructural diagram of metal base plate 2 as seen from its lower surfaceside. In the figure, depression 82 is provided in the form of a slit inmetal base plate 2. The outer side (outer periphery) of projection anddepression 8 is surrounded by projecting peripheral portion 7. Here, thewidth of metal base plate 2 in the X direction is represented by W, thewidth of projection 81 and depression 82 is represented by W1, thethickness of projection 81 is represented by L1, and the gap ofdepression 82 is represented by S1. The width of projecting peripheralportion 7 surrounding projection and depression 8 is represented by W2and the thickness thereof is represented by L2, where W2=L2 issatisfied. However, W2 and L2 do not need to be the same size as long asperipheral portion 7 can produce the effect of suppressing thedeformation of metal base plate 2. The subsequent schematic planarstructural diagrams represent the lower surface side of the metal baseplate.

The dimension of W2 may be set to be greater (thicker) than L1 so as tosuppress the deformation of metal base plate 2. For example, thedimension of W2 may be twice or more as great as L1, and can be selectedas appropriate depending on the size and heat dissipation performance ofmetal base plate 2. When L1 is 0.5 mm, W2 can be set to 1 mm or more,such as 1.5 mm or 2 mm. When W2 is 1 mm or less, the effect ofsuppressing the deformation of metal base plate 2 during transfermolding is lessened, and W2 is therefore desirably 1 mm or more.

The dimension of W2 satisfies a relation of W1≥6×W2. When W1 is ¾ orless of W, the strength of projection and depression 8 cannot be ensuredupon swaging of heat dissipation fin 6. Thus, it may not be possible tohold heat dissipation fin 6. When W1 is ¾ or more of the width of metalbase plate 2, on the other hand, the strength of projection anddepression 8 can be ensured even upon swaging of heat dissipation fin 6.It is then possible to keep holding heat dissipation fin 6. Again inthis case, the dimension of W2 can be selected as appropriate dependingon the size and the like of metal base plate 2.

Projections 81 provided on the lower surface of metal base plate 2 arealigned such that their respective surfaces in the width direction faceone another in one direction, as shown in FIG. 2, and the outerperipheral portion of these projections and depressions 8 is surroundedby flat and projecting peripheral portion 7. Depressions 82 are providedin the form of slits. Furthermore, while it is preferable thatperipheral portion 7 has a constant (equal) height, it is notnecessarily required for projections 81 of projections and depressions 8to have a height identical to the height of peripheral portion 7. Thatperipheral portion 7 has an equal height means that, once metal baseplate 2 is mounted in a molding die with its upper surface on whichinsulating sheet 3 has been formed as the upper side, the surface ofinsulating sheet 3 is flat with respect to the mounting surface of metalbase plate 2. To suppress the deformation (warpage) by pressure duringresin molding, however, it is desirable that some of projections 81 havea height identical to the height of peripheral portion 7.

The height of heat dissipation fin 6 and the height of projection 81 aredefined in the X direction, the width of projection 81 and depression 82is defined in the X direction, and the thickness (L1) of projection 81and the gap (S1) of depression 82 are defined in the Y direction. S1needs to have a width that permits heat dissipation fin 6 to be insertedinto S1, depending on the thickness of heat dissipation fin 6. L1 needsto have a width that permits heat dissipation fin 6 to be inserted intoS1 and swaged. S1 and L1 may be the same width or different widths, andmay be set to dimensions that permit their functions to be carried out.

FIG. 3 is a schematic diagram of a heat dissipation fin in the firstembodiment of this invention. FIG. 4 is a schematic diagram of anotherheat dissipation fin in the first embodiment of this invention. FIG. 5is a schematic diagram of another heat dissipation fin in the firstembodiment of this invention. FIG. 6 is a schematic diagram of anotherheat dissipation fin in the first embodiment of this invention. In thefigures, heat dissipation fins 60, 61, 62 and 63 include protrusions600, 610, 620 and 630 of width W1 each inserted into depression 82 ofprojection and depression 8. By inserting each of these protrusions 600,610, 620 and 630 into depression 82 of projection and depression 8, heatdissipation fins 60, 61, 62 and 63 are mounted on metal base plate 2.Heat dissipation fins 61, 62 and 63 have portions wider than protrusions610, 620 and 630.

FIG. 7 is a schematic sectional structural diagram of another metal baseplate in the first embodiment of this invention. FIG. 8 is a schematicplanar structural diagram of the another metal base plate in the firstembodiment of this invention, as seen from its lower surface side. Inthe figures, the outer peripheral portion of peripheral portion 7 isprovided with a step 9. This step 9 is formed in a direction from thelower surface toward the upper surface of metal base plate 2. To improvethe reliability of semiconductor device 100, it is more preferable thatsealing resin 5 have a locking structure to lock metal base plate 2,instead of merely covering the side surfaces of metal base plate 2.While the outer peripheral portion of peripheral portion 7 has step 9 tostructurally provide a projection and a depression in FIG. 7, theportion of this step 9 at the outer peripheral portion will be coveredby sealing resin 5 after transfer molding, leading to a structure tolock metal base plate 2.

This step 9 causes sealing resin 5 to wrap around the lower surface sideof metal base plate 2 during transfer molding. Step 9 does not need tohave a depth of depression 82 (step height from the lower surface sideto the upper surface side) for the insertion of heat dissipation fin 6.The step only needs to permit sealing resin 5 to wrap around the lowersurface of metal base plate 2 during transfer molding. The structureprovided with such step 9 can achieve the effect of suppressingexfoliation of sealing resin 5 and insulating sheet 3 starting from theend portion of metal base plate 2. Sealing resin 5 that has wrappedaround the lower surface side of metal base plate 2 is formed only atthe portion of step 9. Thus, step 9 is not a projection-and-depressionstructure involved with the insertion of such heat dissipation fin 6.While step 9 is formed at peripheral portion 7 in the direction from thelower surface toward the upper surface of metal base plate 2, the effectof suppressing the exfoliation of sealing resin 5 by anchoring effect isachieved also when step 9 is formed on the side surfaces of peripheralportion 7, for example.

FIG. 9 is a schematic planar structural diagram of another metal baseplate in the first embodiment of this invention. FIG. 9 is a schematicplanar structural diagram of metal base plate 2 as seen from its lowersurface side. In the figure, depression 82 is provided in the form of aslit in metal base plate 2. The outer side (outer periphery) ofprojection and depression 8 is surrounded by projecting peripheralportion 7. Furthermore, metal base plate 2 includes a projection 83 in aportion of projection 81. This projection 83 may have the same height asperipheral portion 7, or may have the same height as projection 81. Thethickness of projection 83 can be made greater than the thickness ofprojection 81, to increase the strength of metal base plate 2.

In either case of the height of projection 83, the warpage of metal baseplate 2 by pressure during transfer molding can be suppressed. For thismetal base plate 2, similar heat dissipation fins 60, 61, 62 and 63 thatcan be inserted into metal base plate 2 can be used.

FIG. 10 shows schematic structural diagrams of another metal base platein the first embodiment of this invention. FIG. 10(a) is a schematicplanar structural diagram of metal base plate 2. FIG. 10(b) is aschematic sectional structural diagram of metal base plate 2 along achain-dotted line B-B in FIG. 10(a). In the figures, projection anddepression 8 have a shape provided with projections 83 and 84 forreinforcing metal base plate 2. Projection 84 is provided in a directionintersecting projection and depression 8. The direction intersectingprojection and depression 8 may be orthogonal to projection anddepression 8, or may be a diagonal direction of metal base plate 2.

The width of projection 84 may be the same as the thickness ofprojection 83, for example. The thickness of projection 83 and the widthof projection 84 do not necessarily need to have the same size, and mayhave such sizes as to contribute to the reinforcement of metal baseplate 2. The width of projection 84 may be the same as the width ofperipheral portion 7. The height of these projections 83 and 84 may bethe same as the height of peripheral portion 7, or may be the same asthe height of projection and depression 8. In particular, the strengthof metal base plate 2 can be increased even when the height ofprojection 84 is only slightly greater than a bottom surface ofdepression 82, as shown in FIG. 10(b). Again in this case, when the heatdissipation fin is inserted into depression 82, a structure is providedin which the heat dissipation fin is supported by substantially theentire surfaces of projections 81 in the width direction. Such a shapepermits transfer molding at higher pressure.

FIG. 11 is a schematic diagram of another heat dissipation fin in thefirst embodiment of this invention. FIG. 12 is a schematic diagram ofanother heat dissipation fin in the first embodiment of this invention.FIG. 13 is a schematic diagram of another heat dissipation fin in thefirst embodiment of this invention. FIG. 14 is a schematic diagram ofanother heat dissipation fin in the first embodiment of this invention.In the figures, heat dissipation fins 601, 611, 621 and 631 includeprotrusions 6010, 6110, 6210 and 6310 each inserted into depression 82of projection and depression 8 shown in FIG. 10. Heat dissipation fins601, 611, 621 and 631 have shapes that can be inserted into metal baseplate 2 shown in FIG. 10.

FIG. 15 shows the shape of a swaging portion of the heat dissipation finof the metal base plate in the first embodiment of this invention. Inthe figure, a swaging portion 13 is provided during swaging of heatdissipation fin 6 to projection and depression 8. Swaging portion 13 isprovided in depression 82 sandwiched between two opposite projections81, has a protruding wall lower in height than projection 81, and swagesheat dissipation fin 6 by this protruding wall and projection 81. Here,two protruding walls are provided in depression 82 for swaging heatdissipation fins 6, with a groove formed between these protruding walls.

Next, a method of manufacturing semiconductor device 100 of the firstembodiment configured as described above is described. Basically,semiconductor device 100 can be fabricated with a manufacturing methodsimilar to a conventional manufacturing method, but is different from aconventional manufacturing method in a metal member forming step and atransfer molding step.

FIGS. 16 to 21 are schematic sectional structural diagrams of steps ofmanufacturing the semiconductor device in the first embodiment of thisinvention. FIG. 16 is a schematic sectional structural diagram showing ametal member forming step. FIG. 17 is a schematic sectional structuraldiagram showing an insulating layer forming step. FIG. 18 is a schematicsectional structural diagram showing a metal layer forming step. FIG. 19is a schematic sectional structural diagram showing a semiconductorelement joining step. FIG. 20 is a schematic sectional structuraldiagram showing a sealing resin curing step. FIG. 21 is a schematicsectional structural diagram showing a fin inserting step. Semiconductordevice 100 can be manufactured by the steps from FIGS. 16 through 21.When heat dissipation fin 6 is not used, semiconductor device 100 iscompleted by the steps through FIG. 20. FIG. 22 shows schematicsectional structural diagrams during transfer molding in the firstembodiment of this invention. FIG. 23 is a schematic sectionalstructural diagram during another transfer molding in the firstembodiment of this invention.

In the figures, projecting peripheral portion 7 of metal base plate 2 isdisposed in contact with a bottom surface 10 a of a molding die 10. FIG.22 shows an example structure in which projection and depression 8 arein contact with bottom surface 10 a of molding die 10. FIG. 23 shows anexample structure in which projection and depression 8 are not incontact with bottom surface 10 a of molding die 10. FIG. 22(a)represents a state in which metal base plate 2 has been disposed inmolding die 10, and FIG. 22(b) represents a state in which sealing resin5 has been press-fitted into molding die 10.

First, as shown in FIG. 16, depressions 82 in the form of slits (in theform of lines) are formed at prescribed intervals on the lower surface(the other surface) of metal base plate 2 made of aluminum or the like.Here, if swaging is to be used as a method of fixing heat dissipationfin 6, the shape of projection and depression 8 may be devised toinclude swaging portion 13 as shown in FIG. 15, to facilitate theswaging of heat dissipation fin 6 to semiconductor device 100 (metalbase plate 2). Depressions 82 in the form of slits are formed so as notto penetrate to the outermost periphery (peripheral portion 7) of thelower surface of metal base plate 2, and the outermost periphery(peripheral portion 7) is formed to have a constant height. Accordingly,projecting peripheral portion 7 is formed to surround projection anddepression 8. A tip end portion of projection 81 of projection anddepression 8 provided in the form of a slit is set to a height equal toor lower than the height of projecting peripheral portion 7 (metalmember forming step).

Metal base plate 2 may be formed by being cut from a metal block, or maybe integrally formed using a die. Here, peripheral portion 7 formed inmetal base plate 2 is formed at a constant height within ranges of theaccuracy of surface leveling of the metal block and the accuracy of thedie.

Next, as shown in FIG. 17, insulating sheet 3 is formed by applyingepoxy-based resin to the upper surface (one surface) of metal base plate2 opposite to the surface provided with projection and depression 8(insulating layer forming step). Next, as shown in FIG. 18, metal wiringpattern 4 can be formed by laminating a copper plate, for example, oninsulating sheet 3, and an etching process and the like thereafter(metal layer forming step).

Next, as shown in FIG. 19, solder paste (not shown) is applied to aprescribed position of this metal wiring pattern 4, and an electroniccomponent such as semiconductor element 1 is joined and mounted on thissolder paste by a reflow process and the like. That is, metal base plate2 provided with projection and depression 8 is heated to hightemperature to melt the applied solder paste under the high temperature,thereby electrically connecting the electronic component such assemiconductor element 1 and metal wiring pattern 4 (semiconductorelement joining step).

Next, metal wiring pattern 4 and semiconductor element 1 areelectrically connected by a bonding wire (not shown) which is a metalwire (metal wire forming step). While a bonding wire is used here, anywire may be used as long as they can be electrically connected.

Next, to resin-seal the entirety of semiconductor element 1, metalwiring pattern 4, insulating sheet 3 and the like by transfer moldingusing sealing resin 5, as shown in FIG. 22(a), metal base plate 2 ismounted in molding die 10 by bringing bottom surface 10 a of molding die10 into contact with peripheral portion 7 (metal member mounting step).

Next, as shown in FIG. 22(b), sealing resin 5 is poured by a transfermolding machine (sealing step). Accordingly, the members formed on metalbase plate 2 are sealed with sealing resin 5. Sealing resin 5 covers theentire side surfaces of metal base plate 2. Accordingly, the outerperipheral side surfaces of peripheral portion 7 are also covered bysealing resin 5. Here, since peripheral portion 7 is continuously formedto surround projection and depression 8, sealing resin 5 is preventedfrom flowing into projection and depression 8 during transfer molding.It should be noted that FIG. 22 only shows metal base plate 2 and alower die half of molding die 10, a portion above insulating sheet 3 notbeing shown.

Here, sealing resin 5 may be poured in a reduced-pressure atmosphere,whereby the formation of voids in sealing resin 5 can be suppressed. Asshown in FIG. 20, sealing resin 5, which is thermosetting resin such asepoxy resin, is cured by heating within molding die 10, and can beremoved from molding die 10 after a certain period of time (sealingresin curing step). Subsequently, additional heat treatment may beperformed in an oven or the like as needed, in order to furtherfacilitate the curing of sealing resin 5.

The steps up until the resin sealing by transfer molding are not limitedto this process. A method may be employed in which metal base plate 2provided with insulating sheet 3 before the curing of sealing resin 5 onthe upper surface of metal base plate 2 opposite to the surface providedwith projection and depression 8, and a lead frame having the electroniccomponent such as semiconductor element 1 mounted thereon in advance bya reflow process and the like can be mounted in molding die 10, andsealing resin 5 is poured by the transfer molding machine, wherebyinsulating sheet 3 is heated, pressed and cured.

Lastly, as shown in FIG. 21, heat dissipation fin 6 is inserted intodepression 82, to complete semiconductor device 100. Heat dissipationfin 6 may be attached depending on the amount of heat generation insemiconductor device 100, and does not need to be attached if the heatcan be dissipated by projection and depression 8 (fin inserting step).Heat dissipation fin 6 can be fixed to depression 82 by an insertionmethod using swaging, brazing, or a fixing member.

Here, problems with the use of a metal base plate having a conventionalstructure will be described using FIGS. 24 to 26.

FIG. 24 is a schematic planar structural diagram of a metal base platehaving a conventional structure. FIG. 25 is a schematic sectionalstructural diagram of the metal base plate having the conventionalstructure. FIG. 25 is a schematic sectional structural diagram along achain-dotted line A-A in FIG. 24. FIG. 26 shows schematic sectionalstructural diagrams during transfer molding using the metal base platehaving the conventional structure. FIG. 26(a) represents a state inwhich a metal base plate 21 has been disposed in a molding die 101, andFIG. 26(b) represents a state in which sealing resin 5 has beenpress-fitted into molding die 101. In the figures, metal base plate 21has a projection and a depression 80 having a projection 85 and adepression 86. Metal base plate 21 is disposed in molding die 101.

When projections 85 (depressions 86) are aligned in one direction at alower surface (the other surface) of metal base plate 21, the outermostperiphery of the lower surface of metal base plate 21 is provided with aflat portion 71, as shown in FIG. 25, in order to achieve moldingwithout causing leakage of sealing resin 5 to projection and depression80 in a transfer molding step. Resin molding is performed while thisflat portion 71 is pressed as a sealing surface against molding die 101as shown in FIG. 26.

Here, if importance is attached to the sealing performance during resinmolding, a clearance is needed between tip end portions of projections85 of projections and depressions 80 and a bottom surface 101 a ofmolding die 101, in consideration of manufacturing dimensional variationamong the tip end portions of projections 85 (see FIG. 26(a)). Whenresin molding is performed with this clearance being provided, metalbase plate 21 is deformed (warped) due to resin molding pressure (seeFIG. 26(b)). Accordingly, exfoliation or cracks may occur in insulatingsheet 3 provided on metal base plate 21, resulting in reducedreliability of a semiconductor device including this metal base plate21.

In semiconductor device 100 having the structure of metal base plate 2of the present first embodiment, however, the outermost periphery of thelower surface of metal base plate 2 provided with projection anddepression 8 is provided with projecting peripheral portion 7 of aconstant height to surround projection and depression 8. Accordingly,sealing resin 5 can be prevented from flowing toward projection anddepression 8 during resin molding. In addition, heat dissipation fin 6is inserted into depression 82 of projection and depression 8 after theresin molding, thereby increasing the heat dissipation properties.Furthermore, with the structure that suppresses the deformation of metalbase plate 2 as compared to a conventional structure, higher resinmolding pressure than was conventionally possible can be achieved,thereby permitting the application of insulating sheet 3 having higherheat dissipation performance.

In the semiconductor device configured as above, since projectingperipheral portion 7 is provided to surround projection and depression 8formed on the lower surface of metal base plate 2, the warpage of metalbase plate 2 due to molding pressure during transfer molding can bereduced, and the occurrence of exfoliation of and cracks in insulatingsheet 3 formed on the upper surface of metal base plate 2 can besuppressed, thereby improving the reliability of the semiconductordevice.

In addition, the reduced warpage of metal base plate 2 permits resinmolding at higher molding pressure than was conventionally possible,thereby permitting the application of insulating sheet 3 having higherthermal conductivity than in conventional technique where the pressurewas required to carry out the function.

Second Embodiment

The present second embodiment is different in that insulating sheet 3having a higher thermal conductivity than that of insulating sheet 3which is an insulating layer in the first embodiment is employed. Byemploying insulating sheet 3 having a higher thermal conductivity inthis manner, the heat dissipation properties of the semiconductor devicecan be improved while the reliability of semiconductor device ismaintained.

Insulating sheet 3 is formed, for example, by filling thermosettingresin such as epoxy resin with inorganic powders such as silica,alumina, boron nitride, or aluminum nitride, used either alone or as amixture, which has high thermal conductivity for improving the heatdissipation properties. Insulating sheet 3 having higher heatdissipation properties needs to be more highly filled with the inorganicpowders, and is filled with boron nitride or aluminum nitride havinghigher thermal conductivity among the inorganic powders. However, toensure the inherent thermal conductivity and insulation properties ofinsulating sheet 3, filling with a higher amount of inorganic powdersrequires curing under higher pressure during heating and curing of theresin such as epoxy resin serving as a base of insulating sheet 3.

In particular, the shape of inorganic powders has a significant effect.When boron nitride having high thermal conductivity is used, since itspowders are scale-shaped, higher pressure is often required to attainthe inherent properties than when other powders having a crushed shapeor spherical shape such as silica or alumina are used for the filling.When insulating sheet 3 is heated, pressed and cured within the transfermolding machine, insulating sheet 3 having higher thermal conductivitycan be applied by using metal base plate 2 of the present invention.

When boron nitride is used as the inorganic powders to fill insulatingsheet 3, where the inorganic powders are in an amount of less than 40volume % including the boron nitride, the inherent thermal conductivityand insulation properties can be ensured at a molding pressure of about5 MPa during the heating and curing, and the thermal conductivity isabout 2 to 5 W/(m·K). Where the inorganic powders are in an amount of 40volume % or more and less than 50 volume %, a molding pressure of about10 MPa is required, and the thermal conductivity is about 4 to 6W/(m·K). Here, when metal base plate 21 having the conventionalstructure shown in FIGS. 24 to 26 is used, cracks may occur ininsulating sheet 3 during resin molding, which may result in asignificantly reduced breakdown voltage although the thermalconductivity manifests itself.

Moreover, when the inorganic powders in an amount of 50 volume % or moreand less than 60 volume % including boron nitride is used for thefilling, a thermal conductivity of about 5 up to 14 W/(m·K) can manifestitself, but a molding pressure of 10 MPa or more is required, and asemiconductor device having higher reliability can be obtained byapplying the structure of the present invention. It should be noted thatthe thermal conductivity varies depending on whether the boron nitrideis used as a simple substance, or as mixed with other powders, as theinorganic powders for the filling, which can be appropriately selectedas needed.

In the semiconductor device configured as above, since projectingperipheral portion 7 is provided to surround projection and depression 8formed on metal base plate 2, the warpage of metal base plate 2 due tomolding pressure during transfer molding can be reduced, and theoccurrence of exfoliation of and cracks in insulating sheet 3 formed onthe upper surface of metal base plate 2 can be suppressed, therebyimproving the reliability of the semiconductor device.

In addition, the reduced warpage of metal base plate 2 permits resinmolding at higher molding pressure than was conventionally possible,thereby permitting the application of insulating sheet 3 having higherthermal conductivity than in conventional technique where the pressurewas required to carry out the function.

Third Embodiment

The present third embodiment is different in that insulating sheet 3used in the first embodiment is replaced by a ceramic substrate 31. Wheninsulating sheet 3 is changed to ceramic substrate 31 in this manner,the warpage of ceramic substrate 31 can again be suppressed, therebyimproving the reliability of the semiconductor device.

FIG. 27 is a schematic sectional structural diagram of a semiconductordevice in the third embodiment of this invention. It should be notedthat FIG. 27 is a sectional view schematically showing a configurationof the semiconductor device, and therefore shows positional relation ofrespective parts, components, and the like in an overview manner.

In the figure, a semiconductor device 200 includes semiconductor element1, metal base plate 2 which is a metal member, ceramic substrate 31which is an insulating layer, metal wiring patterns 4 and 11 which aremetal layers, sealing resin 5, heat dissipation fin 6 which is a fin,peripheral portion 7, projection and depression 8, projection 81, anddepression 82. An insulating substrate 12 includes metal wiring patterns4 and 11 on opposite surfaces of ceramic substrate 31.

Ceramic substrate 31 can be used, other than insulating sheet 3, for aportion corresponding to the insulating layer. When applied to metalbase plate 21 as shown in FIG. 25, there was a problem of the occurrenceof cracks in ceramic substrate 31 due to the deformation of metal baseplate 21 during the molding as shown in FIG. 26, resulting indeteriorated insulation properties. However, with this structure asshown in FIG. 27, a semiconductor device having high insulationreliability can be obtained even when ceramic substrate 31 is applied.

When ceramic substrate 31 is used, metal wiring pattern 4 is formed inadvance on an upper surface of ceramic substrate 31, and semiconductorelement 1 is joined and mounted on this metal wiring pattern 4 withsolder (not shown). In addition, metal wiring pattern 11 is formed inadvance on a lower surface of ceramic substrate 31. Metal wiringpatterns 4 and 11 are formed on the opposite surfaces of ceramicsubstrate 31, to thereby form insulating substrate 12. Furthermore,ceramic substrate 31 having metal wiring patterns 4 and 11 formed on itsopposite surfaces is joined to metal base plate 2 by joining metalwiring pattern 11 and metal base plate 2 to each other with solder (notshown). Then, sealing resin 5 can be poured by the transfer moldingmachine to manufacture semiconductor device 200. Basically,semiconductor device 200 can be manufactured by the manufacturing stepsdescribed in the first embodiment, by changing insulating sheet 3 toinsulating substrate 12 (ceramic substrate 31).

In the semiconductor device configured as above, since projectingperipheral portion 7 is provided to surround projection and depression 8formed on the lower surface of metal base plate 2, the warpage of metalbase plate 2 due to molding pressure during transfer molding can bereduced, and the occurrence of exfoliation of and cracks in ceramicsubstrate 31 (insulating substrate 12) formed on the upper surface ofmetal base plate 2 can be suppressed, thereby improving the reliabilityof the semiconductor device.

REFERENCE SIGNS LIST

-   -   1 semiconductor element; 2, 21 metal base plate; 3 insulating        sheet; 4, 11 metal wiring pattern; 5 sealing resin; 6, 60, 61,        62, 63, 601, 611, 621, 631 heat dissipation fin; 7 peripheral        portion; 8, 80 projection and depression; 9 step; 10, 101        molding die; 10 a, 101 a bottom surface of molding die; 12        insulating substrate; 13 swaging portion; 31 ceramic substrate;        71 flat portion; 81, 83, 84, 85 projection; 82, 86 depression;        100, 200 semiconductor device; 600, 610, 620, 630, 6010, 6110,        6210, 6310 protrusion.

The invention claimed is:
 1. A semiconductor device comprising: a metalmember provided, on a lower surface of the metal member, withprojections and depressions alternately arranged and aligned such thatsurfaces of the projections in a width direction face one another in onedirection, a projecting peripheral portion surrounding the projectionsand the depressions and having a height greater than or equal to aheight of each of the projections of the projections and thedepressions; and protruding portions provided in the depressions of theprojections and the depressions in a direction intersecting the widthdirection of the projections, the protruding portions protruding frombottom surfaces of the depressions of the projections and thedepressions and each having a height greater than a height of the bottomsurfaces of the depressions of the projections and the depressions andsmaller than the height of the projections of the projections and thedepressions; an insulating layer formed on an upper surface of the metalmember; a metal layer formed on an upper surface of the insulatinglayer; a semiconductor element joined to an upper surface of the metallayer; and a sealing resin to seal the semiconductor element, the metallayer and the insulating layer, wherein each of the depressions extendsin the width direction from a first side of the projecting peripheralportion to an opposing side of the projecting peripheral portion, awidth in the width direction of each of the depressions is wider than awidth of the depressions in a direction intersecting the widthdirection, one of the protruding portions is arranged in each of thedepressions, each of the depressions having the one protruding portionis configured to receive a fin oriented longitudinally in the widthdirection, and the one protruding portion is configured to cooperatewith receiving the fin and with fixing the fin.
 2. The semiconductordevice according to claim 1, wherein the height of the peripheralportion is constant.
 3. The semiconductor device according to claim 1,wherein a fin is inserted into the depression of the projection and thedepression.
 4. The semiconductor device according to claim 3, whereinthe fin has a portion wider in a width direction than its portioninserted into the depression of the projection and the depression. 5.The semiconductor device according to claim 3, wherein: the fin has awidth substantially equal to a width of the depression, the fin has anotch in one side corresponding to the one protruding portion, and theone side is inserted in the depression.
 6. The semiconductor deviceaccording to claim 1, wherein the projection of the projection and thedepression includes projections of different thicknesses.
 7. Thesemiconductor device according to claim 1, wherein the peripheralportion is provided with a step at its outer peripheral portion.
 8. Thesemiconductor device according to claim 1, wherein the insulating layeris an insulating sheet.
 9. The semiconductor device according to claim8, wherein the insulating sheet includes boron nitride, and is filledwith an inorganic powder material in an amount of 40 volume % or more.10. The semiconductor device according to claim 1, wherein theinsulating layer is a ceramic substrate.
 11. The semiconductor deviceaccording to claim 1, wherein a width in the width direction of each ofthe protruding portions provided in the depressions of the projectionsand depressions being less than a sum of a width in the width directionof the projecting peripheral portion and a width in the width directionof a respective depression portion located between the projectionsprovided in the depressions and the projections and the projectionperipheral portion.
 12. The semiconductor device according to claim 11,wherein a width of each of the protruding portions provided in thedepressions of the projections and the depressions is the same as thewidth of the projecting peripheral portion.
 13. The semiconductor deviceaccording to claim 1, wherein, in a direction in which the projectionsproject from the metal member, a height of the metal member on theprotruding portions is higher than a height of the metal member on thedepressions.